CVE-2018-8796 in rdesktop
Summary
by MITRE
rdesktop versions up to and including v1.8.3 contain an Out-Of-Bounds Read in function process_bitmap_updates() that results in a Denial of Service (segfault).
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Analysis
by VulDB Data Team • 07/06/2023
The vulnerability identified as CVE-2018-8796 represents a critical out-of-bounds read condition within the rdesktop remote desktop protocol client software. This issue affects versions up to and including rdesktop v1.8.3, where the flaw manifests specifically within the process_bitmap_updates() function. The vulnerability stems from inadequate input validation and memory boundary checking when processing bitmap update data streams from remote desktop servers. When a maliciously crafted bitmap update is received during an RDP session, the function fails to properly verify array bounds before accessing memory locations, leading to unpredictable behavior and system instability. The out-of-bounds read occurs during the processing of graphical updates that are part of the RDP protocol's bitmap compression and transmission mechanisms, which are essential for displaying remote desktop content. This vulnerability directly relates to CWE-125, which describes out-of-bounds read conditions in software implementations, and falls under the broader category of memory safety issues that can lead to system crashes or potential exploitation. The flaw demonstrates a classic buffer over-read scenario where the application attempts to access memory beyond the allocated buffer boundaries, potentially causing segmentation faults and application termination.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be exploited by remote attackers to disrupt RDP sessions and potentially gain unauthorized access to systems. When the process_bitmap_updates() function encounters malformed bitmap data, the out-of-bounds read causes the rdesktop client to crash with a segmentation fault, effectively terminating the remote desktop session. This denial of service condition can be particularly problematic in enterprise environments where RDP is commonly used for remote administration and access to critical systems. The vulnerability's exploitation requires minimal privileges since it can be triggered through normal RDP communication protocols, making it a significant concern for network security. Attackers can craft specially formatted bitmap updates that, when processed by the vulnerable rdesktop client, will cause the application to access invalid memory addresses, resulting in immediate system termination. The segmentation fault that occurs represents a direct violation of the application's memory management protocols and can be leveraged to disrupt availability of remote desktop services, potentially affecting business continuity and system accessibility.
Mitigation strategies for CVE-2018-8796 should focus on immediate software updates and network-level protections. The most effective solution involves upgrading to rdesktop version 1.8.4 or later, where the out-of-bounds read vulnerability has been patched through proper input validation and boundary checking mechanisms. System administrators should implement comprehensive patch management procedures to ensure all affected rdesktop installations are updated promptly. Network segmentation and access controls can provide additional defense-in-depth measures by limiting exposure of RDP services to trusted networks and implementing strict authentication requirements. Monitoring for unusual RDP traffic patterns and implementing intrusion detection systems can help identify potential exploitation attempts. The vulnerability also highlights the importance of input sanitization and memory safety practices in network protocol implementations, aligning with ATT&CK technique T1210 for exploitation of remote services through malformed data inputs. Organizations should consider implementing network access control lists to restrict RDP access to authorized personnel only and maintain regular vulnerability assessments to identify similar memory safety issues in other remote desktop and network protocol implementations. Additionally, deploying application whitelisting solutions and implementing mandatory access controls can reduce the attack surface for exploitation of such vulnerabilities.